The William Bonner, who was John M. Bonner's brother was probably Corporal William Bonner, Co. I, 7th Ala. Cavalry Regiment. Cpl., the abbreviation for corporal, is often mistaken for Cpt., for Captain. This fits the birth year reasonably. Was this company a Pickens County, Alabama, unit? That may clinch it. I think he was a doctor postwar, and joined John in Morehouse Parish, Louisiana.